Method and apparatus for device-to-device communication

ABSTRACT

A first user equipment (UE) receives information regarding a signal configuration from a network entity on a first carrier, and a reference signal from a second UE on a second carrier. The second carrier is associated with a transmission bandwidth configuration and a channel bandwidth. The transmission bandwidth configuration of the second carrier is contained within the channel bandwidth of the second carrier. The reference signal is within the channel bandwidth of the second carrier and in proximity to an edge of the transmission bandwidth configuration of the second carrier.

TECHNICAL FIELD

The disclosure relates to device-to-device communication in a wirelessnetwork.

BACKGROUND

The demand for data capacity in wireless networks has increaseddramatically with the widespread use of smartphones and tabletcomputers. In addition to traditional voice services, consumers nowexpect to be able to use their wireless devices to watch streamingvideo, often in a high-definition format, play on-line games inreal-time, and transfer large files. This has put additional load onwireless networks and, in spite of advances in cellular technology(e.g., the deployment of 4G networks, the use of newer versions of theIEEE 802.11 family of standards), capacity is still an issue thatproviders have to consider.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of a communication system in which variousembodiments of the invention may be implemented.

FIG. 2 is a block diagram depicting certain aspects of a network entityin accordance with an embodiment of the invention.

FIG. 3 is a block diagram depicting aspects of a UE in an embodiment ofthe invention.

FIG. 4A is a frame structure according to an embodiment of theinvention.

FIG. 4B is a resource block according to an embodiment of the invention.

FIG. 5 is an uplink subframe according to an embodiment of theinvention.

FIG. 6 is a downlink subframe according to an embodiment of theinvention.

FIG. 7A is a carrier according to an embodiment of the invention.

FIG. 7B is an aggregation of component carriers according to anembodiment of the invention.

FIG. 8A is a wireless network according to an embodiment of theinvention.

FIG. 8B shows a frame, subframe, and special subframe according to anembodiment of the invention.

FIGS. 9, 10, and 11 show a D2D communication scheme according to anembodiment of the invention.

FIGS. 12, 13, 15, and 16 depict steps taken during D2D communicationaccording to various embodiments of the invention.

FIG. 14 depicts HARQ buffering according to an embodiment of theinvention.

DESCRIPTION

Cellular networks such as LTE and UMTS have traditionally operated on amodel in which the network controls radio communications. For example,assume that UE1 and UE2 operate in a traditional cellular network, andthat the network includes eNB1 and eNB2, with UE1 being connected toeNB1, and UE2 being connected to eNB2. When UE1 transmits data that isintended for UE2, the data travels from UE1 to eNB1, which relays thedata to eNB2. The eNB2 then relays the message to UE2. Thus, it takes atleast two hops (UE1->eNB1) (eNB2->UE2) on the cellular network for datato get from UE1 to UE2. There may also be further delay resulting fromadditional hops being needed for routing. Such delays may occur even ifthe two UEs are connected to the same eNB.

However, if the UEs are able to communicate directly with one anotherusing so-called Device-to Device (D2D) communication, it would take onlyone hop (UE1->UE2) for data to get from UE1 to UE2.

In an embodiment of the invention, UEs communicate directly with oneanother without passing through a network or other intermediate entity.To carry out such D2D communication, the UEs use resources (e.g.,cellular spectrum) of the network. The UEs may, however, maintain theirusual connections to the network (e.g., each UE may still be connectedto an eNB of a cellular network).

Benefits of D2D communication in a cellular network include (1)increased cellular system throughput (e.g., D2D traffic uses fewerresources to communicate same amount of data), and (2) improved userexperience (e.g., faster data transfer and reduced latency).

In accordance with the foregoing, a method and apparatus fordevice-to-device communication is provided. According to an embodimentof the invention, a first user equipment (UE) receives informationregarding a signal configuration from a network entity on a firstcarrier, and a reference signal from a second UE on a second carrier.The second carrier is associated with a transmission bandwidthconfiguration and a channel bandwidth. The transmission bandwidthconfiguration of the second carrier is contained within the channelbandwidth of the second carrier. The reference signal is within thechannel bandwidth of the second carrier and in proximity to an edge ofthe transmission bandwidth configuration of the second carrier. Thefirst UE determines a link quality of the received reference signalbased on the signal configuration, and reports the determined linkquality to a network entity via the second carrier.

In further embodiments, the first UE determines, from the referencesignal, a maximum transmission power limit for communication between thefirst and second UE on a third carrier. In response to receiving thepower limit, the first UE limits its overall transmission power levelbased the maximum transmission power limit.

The reference signal may be a beacon signal specifically defined for D2Ddiscovery. It may also be received within an aggregated channelbandwidth, in which the transmission bandwidth configurations of thesecond and third carriers are contained within the aggregated channelbandwidth. The reference signal may be received outside both the firsttransmission bandwidth configuration and the second transmissionbandwidth configuration.

In some embodiments, the resource is within the channel bandwidth of thesecond carrier but outside the transmission bandwidth configuration ofthe second carrier, and the reference signal from the second UE isreceived on the resource. The first and second carriers may be within alicensed spectrum.

The link quality may include information regarding one or more of aReference Signal Received Power (RSRP), Reference Signal ReceivedQuality (RSRQ), Received Signal Strength Indicator (RSSI), and a ChannelState Information (CSI).

The network entity may be the first of at least two network entities,and, in one embodiment, the UE receives information regarding the signalconfiguration on a second carrier from the second network entity. Theinformation may be received in a system information block (SIB).

In an embodiment, the signal configuration includes informationregarding a resource block of the second carrier. The resource block iswithin the channel bandwidth of the second carrier and proximate to anedge of the transmission bandwidth configuration of the second carrier.The first UE may also receive the reference signal from the second UE onthe resource block. The resource block may also be located in a regionof the second carrier that is usable for low power transmissions. Theresource block may also be within the channel bandwidth of the thirdcarrier and proximate to an edge of the transmission bandwidth of thethird carrier.

In some embodiments, the resource block is located outside of thetransmission bandwidth configuration of the second carrier but withinthe channel bandwidth of the second carrier. In others, it is outside ofthe transmission bandwidth configuration of the second carrier, andwithin the channel bandwidth of a third carrier. The third carrier mayor may not include a synchronization signal. The channel bandwidth ofthe third carrier may be less than ⅓ of the channel bandwidth of thesecond carrier. Also, the transmission bandwidth configuration of thethird carrier may within the channel bandwidth of the third carrier.

In an embodiment, the first UE receives, in the first carrier,information regarding a resource of a third carrier and receive datafrom the second UE.

In some embodiments, the signal configuration information indicates thata physical uplink control channel (PUCCH) is over-provisioned such thatthe edge resource blocks that are normally used by the PUCCH areavailable to be used for direct device-to-device communication.

In an embodiment, the first carrier is within a downlink operating bandof a frequency division duplex (FDD) mode operating band, and the secondcarrier is within an uplink operating band of the FDD mode operatingband.

In other embodiments, the first UE receives, on the first carrier,information regarding a maximum transmission power limit forcommunicating with the second UE on the third carrier

The first UE may perform some of the method while camping on a wirelessnetwork, but perform the receiving steps after it is no longer camping,but is still in an idle mode. The first UE may also perform the stepswhile in the active mode.

Another embodiment of the invention is a first UE having a transceiver,a memory, and a processor. The transceiver is configured to receive, ona first carrier, information regarding a signal configuration. Thememory, which is communicatively linked to the transceiver, isconfigured to store the signal configuration. The processor iscommunicatively linked to the memory and to the transceiver, and isconfigured to retrieve the signal configuration from the memory and,using the retrieved signal configuration, control the transceiver todetect a reference signal of a second UE on a second carrier.

Referring to FIG. 1, an example of a wireless communication network inwhich embodiments of the invention may be used will now be described.The network 100 is configured to use one or more Radio AccessTechnologies (RATs), examples of which include an E-UTRA, IEEE 802.11,and IEEE 802.16. The network 100 includes a first cell C1 and a secondcell C2. Possible implementations of C1 and C2 include a cellularnetwork macrocell, a femtocell, a picocell, and a wireless access point.First cell C1 is managed by a first network entity NE1 and second cellC2 is managed by a second network NE2. Possible implementations of anetwork entity include an E-UTRA base station, an eNB, a transmissionpoint, a Remote Radio Head, an HeNB, an 802.11 AP, and an IEEE 802.16base station.

Also shown in FIG. 1 are User Equipments (UE) UE1, UE2, and UE3.Possible implementations of a UE include a mobile phone, a tabletcomputer, a laptop, and an M2M (Machine-to-Machine) device. Each of NE1and NE2 transmits signals to and receives signals from one or more ofthe UEs.

Communication between a network entity and a UE typically occurs whenthe UE is located within the network entity's coverage area. Forexample, NE1 would typically communicate with UE1 and UE2, and NE2 wouldtypically communicate with UE3. In certain circumstances, each networkentity may transmit signals to and receive signals from UEs that areconnected to other network entities. For example, NE1 may be able tocommunicate with UE3 if UE3 is close to NE1's coverage area.

The cells, network entities, and UEs of FIG. 1 are only representative,and are intended to facilitate description. In fact, the network 100 mayhave many cells and network entities and be in communication with manyUEs.

In some embodiments of the invention, C1 or C2 are controlled by asingle network entity, or by multiple network entities that coordinatewith one another, e.g., when Carrier Aggregation (CA) or CoordinatedMultipoint communication (CoMP) is being used. Furthermore, one or moreof C1 and C2 may be a virtual cell. A virtual cell is a cell that iscreated as a result of multiple network entities cooperating. A UEgenerally does not perceive any distinction between a virtual cell and anon-virtual cell.

In an embodiment of the invention, each UE (FIG. 1) is a wirelesscommunication device capable of sending and receiving data via thenetwork entities NE1 and NE2 to and from other elements of the network100. Each UE is also capable of communicating with the other UEs overthe network 100 via one or more of the network entities NE1 and NE2.Additionally, one or both of the UEs is capable of engaging in D2Dcommunication.

In various embodiments, each UE of FIG. 1 is capable of transmittinguser data and control information to one or more of the network entitieson an UL carrier, and receiving data and control signals from one ormore of the network entities on a DL carrier. As used herein, “controlinformation” includes data that UEs and various elements of the network100 use for facilitating information, but that is not intended to beaccessed by a user or by user applications. “User data” as herein refersto data that is intended to be accessed by a user and user applications.

In an embodiment of the invention, the UL carrier is made up of a firstset of RF frequencies, while the DL carrier is made up of a second setof RF frequencies. In some embodiments, the frequencies of the ULcarrier do not overlap with the frequencies of the DL carrier. The ULand DL carriers may be part of spectrum licensed for use by a regulatorybody, such as the Federal Communication Commission (FCC). The UL and DLcarriers may also be assigned for un-licensed use by the regulatorybody.

In one embodiment, at least one of the UL carrier and the DL carrier ismade up of a single block of contiguous frequencies. In anotherembodiment, at least one of the UL carrier and the DL carrier is made upof multiple, non-overlapping blocks of contiguous frequencies.

Referring still to FIG. 1, the network 100 also includes a backhaulsystem (not shown). The backhaul system includes wired and wirelessinfrastructure elements, such a fiber optic lines, that carry signalsaround various parts of the network 100, including among the networkentities. The network 100 also includes a core 106 that controls theoperation of the network 100 using various resources, including billingsystems, home location registers, and internet gateways. Several coreresources are depicted in FIG. 1. In an LTE implementation, resources ofthe core 106 communicate with network entities over E-UTRA and withother networks. Examples of core resources are depicted in FIG. 1.

FIG. 2 illustrates a configuration of a network entity (from FIG. 1) inaccordance with an embodiment of the invention. The network entityincludes a controller/processor 210, a memory 220, a database interface230, a transceiver 240, input/output (I/O) device interface 250, anetwork interface 260, and one more antennas, represented by antenna221. Each of these elements is communicatively linked to one another viaone or more data pathways 270. Examples of data pathways include wires,including wires whose dimensions are measured in microns, and wirelessconnections.

During operation of the network entity, the transceiver 240 receivesdata from the controller/processor 210 and transmits RF signalsrepresenting the data via the antenna 221. Similarly, the transceiver240 receives RF signals via the antenna 221 converts the signals intothe appropriately formatted data, and provides the data to thecontroller/processor 210. The controller/processor 210 retrievesinstructions from the memory 220 and, based on those instructions,provides outgoing data to, or receives incoming data from thetransceiver 240. If needed, the controller/processor can retrieve, froma database via the database interface 230, data that facilitates itsoperation.

Referring still to FIG. 2, the controller/processor 210 can transmitdata to other network entities of the network 100 (FIG. 1) via thenetwork interface 260, which is coupled to the backhaul network. Thecontroller/processor 210 can also receive data from and send data to anexternal device, such as an external drive, via the input/outputinterface 250.

The controller/processor 210 may be any programmable processor. Thecontroller/processor 210 may be implemented, for example, as ageneral-purpose or a special purpose computer, a programmedmicroprocessor or microprocessor, peripheral integrated circuitelements, an application-specific integrated circuit or other integratedcircuits, hardware/electronic logic circuits, such as a discrete elementcircuit, a programmable logic device, such as a programmable logicarray, field programmable gate-array, or the like.

The memory 220 may be implemented in a variety of ways, including asvolatile and nonvolatile data storage, electrical, magnetic opticalmemories, random access memory (RAM), cache, hard drive, or other typeof memory. Data is stored in the memory 220 or in a separate database.The database interface 230 is used by the controller/processor 210 toaccess the database. The database contains any formatting data toconnect UE to the network 100 (FIG. 1). The transceiver 240 creates adata connection with the UE.

The I/O device interface 250 may be connected to one or more inputdevices that may include a keyboard, mouse, pen-operated touch screen ormonitor, voice-recognition device, or any other device that acceptsinput. The I/O device interface 250 may also be connected to one or moreoutput devices, such as a monitor, printer, disk drive, speakers, or anyother device provided to output data. The I/O device interface 250 mayreceive a data task or connection criteria from a network administrator.

The network connection interface 260 may be connected to a communicationdevice, modem, network interface card, a transceiver, or any otherdevice capable of transmitting and receiving signals from the network100. The network connection interface 260 may be used to connect aclient device to the network.

According to an embodiment of the invention, the antenna 221 is one of aset of geographically collocated or proximal physical antenna elementslinked to the one or more data paths 270, each having one or moretransmitters and one or more receivers. The number of transmitters thatthe network entity has is related, to the number of transmit antennasthat the network entity has. The network entity may use the multipleantennas to support MIMO communication.

FIG. 3 illustrates a block diagram of a UE (such as one or more of theUEs depicted in FIG. 1) according to an embodiment of the invention. TheUE includes a transceiver 302, which is capable of sending and receivingdata over the network 100. The transceiver is linked to one or moreantennas 303 that may be configured like the one or more antennas of thenetwork entity of FIG. 2. The UE may support MIMO.

The UE also includes a processor 304 that executes stored programs, aswell as a volatile memory 306, and a non-volatile memory 308. Thevolatile memory 306 and the non-volatile memory 308 are used by theprocessor 304. The UE includes a user input interface 310 that maycomprise elements such as a keypad, display, touch screen, and the like.The UE also includes a display screen and an audio interface 312 thatmay comprise elements such as a microphone, earphone, and speaker. TheUE also includes a component interface 314 to which additional elementsmay be attached, for example, a universal serial bus (USB) interface.Finally, the UE includes a power supply 316.

During operation, the transceiver 302 receives data from the processor304 and transmits RF signals representing the data via the antenna 303.Similarly, the transceiver 302 receives RF signals via the antenna 303,converts the signals into the appropriately formatted data, and providesthe data to the processor 304. The processor 304 retrieves instructionsfrom the non-volatile memory 308 and, based on those instructions,provides outgoing data to, or receives incoming data from thetransceiver 302. If needed, the processor 304 can write to, or read fromthe volatile memory 306, particularly for caching data and instructionsthat the processor 304 requires in order for it to perform itsfunctions.

The user interface 310 includes a display screen, such as atouch-sensitive display, that displays, to the user, the output ofvarious application programs. The user interface 310 additionallyincludes on-screen buttons that the user can press in order to cause theUE to respond. The content shown on the user interface 310 is generallyprovided to the user interface at the direction of the processor 304.Similarly, information received through the user interface 310 isprovided to the processor, which may then cause the UE to react.

Referring again to FIG. 1, the general mode of communication of thenetwork 100 according to an embodiment of the invention will now bedescribed. The network entities and the UEs generally communicate withone another via physical UL channels of the UL carrier and via physicalDL channels of the DL carrier. In an LTE embodiment, the modulationscheme used for communication between the network entities and the UEsdiffers depending on whether the signals are being sent in the ULdirection (travelling from a UE to a network entity) or in the DLdirection (travelling from a network entity to a UE). The modulationscheme used in the DL direction is a multiple-access version of OFDMcalled Orthogonal Frequency-Division Multiple Access (OFDMA). In the ULdirection, Single Carrier Frequency Division Multiple Access (SC-FDMA)or DFT-SOFDM is typically used. In an LTE implementation, the bandwidthof the UL or DL carrier varies depending upon whether carrieraggregation is being used (e.g., up to 20 MHz without CA, or up to 100MHz with CA). In FDD operation, the frequencies in the bandwidth of theUL carrier and the frequencies in the bandwidth of the DL carrier do notoverlap.

Referring to FIG. 4A, an LTE frame structure used for carrying databetween the UEs and the network entities on both UL carriers and DLcarriers according to an embodiment of the invention will now bedescribed. In LTE FDD operation, both uplink and downlink Radio framesare each 10 milliseconds (10 ms) long, and are divided into tensubframes, each of 1 ms duration. Each subframe is divided into twoslots of 0.5 ms each. Each slot contains a number of OFDM symbols, andeach OFDM symbol may have a Cyclic Prefix (CP). The duration of a CPvaries according to the format chosen, but is about 4.7 microseconds inthe example of FIG. 4A, with the entire symbol being about 71microseconds. In the context of time-frequency, the subframe is dividedinto units of RBs, as shown in FIG. 4B. When a normal CP is used, eachRB 402 is 12 subcarriers by 7 symbols (one slot). Each RB (when a normalCP is used), in turn, is composed of 84 REs 404, each of which is 1subcarrier by 1 symbol. However, RBs and REs may be other sizes in otherembodiments. Thus, the terms RE and RB may includes time-frequencyresources of any size. In LTE, an RB or an RB pair is the typical unitto which resource allocations may be assigned for uplink and downlinkcommunications.

Referring to FIG. 5, a UL subframe structure used to carry data from UEsto the network entities over an UL carrier according to an LTEembodiment of the invention will now be described. The horizontal scaleof FIG. 6 represents frequency, while the vertical scale representstime. In LTE, a UE typically transmits data to a network entity on aPhysical Uplink Shared Channel (PUSCH), and typically transmits controlinformation to a network entity on a physical uplink control channel(PUCCH). The PUSCH generally carries user data such as video data (e.g.,streaming video) or audio data (e.g., voice calls) from the UEs to thenetwork entities. A UE may also transmit control information on thePUSCH, such as HARQ feedback, CSI reports. Additionally, a UE cantransmit a scheduling request (SR) on the PUCCH. A UE may also transmita sounding reference signal (SRS), which is not part of any particularchannel.

To request uplink resources from a network entity in an embodiment ofthe invention, a UE transmits a scheduling request to a network entity.Referring to FIG. 6, if the network entity grants the request, itresponds by sending a scheduling grant to the UE. A scheduling grant ispart of the downlink control information (DCI). The network entitytransmits the DCI on a downlink control channel (e.g., a physicaldownlink control channel (PDCCH)). The scheduling grant provides the UEwith parameters that the UE uses to transmit data on the PUSCH. Theseparameters include a data modulation and coding scheme, the transportblock size, a resource allocation (e.g., resource blocks and positionwithin the transmission bandwidth configuration), hopping parameters,power control information, and other control information.

In an embodiment of the invention, there are different PUCCH formats,but regardless of format a PUCCH generally carries control informationfrom the UEs to the network entities. PUCCH resource blocks aretypically located at the edges of the UL carrier, while the RBs inbetween may be used for PUSCH resource assignment. In variousembodiments of the invention described herein, a network entity canconfigure a PUCCH to carry data from UE to UE in D2D communication. Theportion of the PUCCH used for D2D will be referred to as PUCCH-D2D.

The control information transmitted by a UE on the PUCCH includes HARQfeedback, SR, and CSI reports. The UE sends HARQ feedback in order toACK or NACK data that the UE receives from a network entity. An SR isused by the UE to request UL resources from the network 100, includingfrom one or more network entities. CSI reports are used by a UE toreport, to a network entity, information regarding the DL transmissionchannel as seen from the point of view of the UE.

Each CSI report sent by a UE may include one or more of a CQI, a PMI,PTI, and an RI. The UE uses the CQI to indicate the highest MCS that, ifused, would result in DL transmissions having a BLER of no more than10%. The UE uses the PMI to indicate, to the network entity, whichprecoder matrix should be used for DL transmissions. The RI is used bythe UE to recommend the transmission rank (number of transmissionlayers) that should preferably be used for DL transmission to the UE.The PTI distinguishes slow fading environments from fast fadingenvironments.

According to an embodiment of the invention, the UE transmits controlinformation on RB pairs configured for PUCCH-D2D. The PUCCH-D2D RBs donot have to be contiguous. Each RB of a pair may, for example, belocated on opposite ends of the frequency range of the transmissionbandwidth.

A UE may transmit an UL DM-RS and/or SRS during communication with thenetwork. The UL DM-RS is used by a network entity for channel estimationto enable coherent demodulation of the PUSCH and/or PUCCH. The SRS isused by the network entity for channel state estimation to supportuplink channel-dependent scheduling and link adaptation.

Referring to FIG. 6, a time-frequency diagram of a DL subframe used forcarrying data from one or more network entities to a UE on a DL carrierwill now be described. The horizontal scale of FIG. 6 representsfrequency, while the vertical scale represents time. The horizontalscale is divided into multiple blocks of frequency, or OFDM subcarriers(“subcarriers”) that may be allocated for transmission. The verticalscale of FIG. 6 is divided into multiple blocks of time, or OFDM symbols(“symbols”) that may be allocated for transmission. The subframe isdivided into time-frequency resource blocks (RBs). Each RB is twelvesubcarriers by seven symbols typically for normal CP. The subframe is atotal of 1 ms long and is divided into two time slots of 0.5 ms each. Inturn, each RB can be divided into multiple resource elements (REs). EachRE is one subcarrier by one symbol.

The DL subframe includes several types of reference signals. Thereferences signals are transmitted by the network entity to the UE toenable the UE to perform various functions. One such reference signal isChannel State Information Reference Signal (CSI-RS), which is used bythe UE to determine channel-state information (CSI). The UE reports CSIto the network entity. The CSI-RS is not necessarily transmitted in allsubframes.

Referring again to FIG. 6, other reference signals on the UL subframeinclude a Demodulation Reference Signal (DM-RS) with the REs beingreferred to as DM-RS REs. Typically, reference signals corresponding toantenna ports 7 and 8 are multiplexed using Code Division Multiplexing(CDM) or other scheme and are mapped to the same REs in time andfrequency domain. The subframe can also include other reference signalssuch as cell-specific reference signal (CRS), positioning referencesignal (PRS), primary synchronization signal (PSS) and secondarysynchronization signal (SSS) that are distributed in the control regionsand/or user data regions of the sub-frame.

The network entity provides the CSI-RS configuration to the UE via RRCsignaling. The RRC layer in the UE provides the CSI-RS configurationinformation to the physical layer in the UE (e.g., “higher layersignaling”).

Referring to FIG. 7A, the structure of an uplink carrier will now bedescribed. The UL carrier 700 has a channel bandwidth 732 that spans arange of frequencies from a first edge 716 to a second edge 720. Thecarrier 700 also has a range of frequencies that make up a transmissionbandwidth configuration 734. The transmission bandwidth configurationstarts at a first edge 722 and ends at a second edge 724. Between thefirst edge 716 of the channel bandwidth and the first edge 722 of thetransmission bandwidth configuration is a first spectral emissionsregion 708. Between the second edge 720 of the channel bandwidth and thesecond edge 724 of the transmission bandwidth configuration is a secondspectral emissions region 710.

Referring still to FIG. 7A the channel bandwidth 732 is the RF bandwidthsupporting a single RF carrier with the transmission bandwidthconfigured in the uplink or downlink of a cell. The channel bandwidth istypically measured in MHz and is usually used as a reference fortransmitter and receiver RF requirements. The transmission bandwidthconfiguration 734 is the highest transmission bandwidth permitted (e.g.,according to industry standards, or government regulation) for uplink ordownlink in a given channel bandwidth. In some cases (e.g., when thecarrier is an E-UTRA/LTE carrier), transmission bandwidth configurationis measured in Resource Block units.

Referring to FIG. 7B, an aggregated carrier 750 is shown. The carrier750 has an aggregated channel bandwidth 780 and an aggregatedtransmission bandwidth configuration 782. The aggregated carrier 750 ismade up of three component carriers 752, 754, and 756. As shown in FIG.7B, the same elements described in conjunction with FIG. 7A are presentin the carrier 750. Specifically, there are RBs 760 defined in thespectral emission regions outside of the transmission bandwidthconfiguration of each of the three component carriers but within thechannel bandwidths of each of the three carriers.

Referring still to FIG. 7B, the aggregated channel bandwidth 780 is theRF bandwidth in which a UE can transmit and/or receive multiplecontiguously aggregated carriers. The aggregated transmission bandwidthconfiguration 782 is the highest transmission bandwidth permitted (e.g.,according to industry standards, or government regulation) for uplink ordownlink in a given aggregated channel bandwidth. In some cases (e.g.,when the carrier is an E-UTRA/LTE carrier), transmission bandwidthconfiguration is measured in Resource Block units.

Using HARQ

The structure of a soft buffer in the manner in which UEs use the softbuffer in an embodiment of the invention will now be described withreference to FIGS. 3 and 14. Referring to FIG. 3, the transceiver 302receives the signal via a carrier (e.g., a UL carrier, a DL carrier, ora D2D carrier). The transceiver 302 passes the signal to the processor304 which, in this example, is a baseband processor. One or more of thetransceiver 302 and processor 304 includes a signal processing element1400, which is shown in FIG. 14.

The signal processing element 1400 may be implemented in hardware,software, or a combination of the two. The signal processing element1400 is organized into functional blocks. These blocks are depicted inFIG. 14, and their functions will now be described. The signal isreceived by the transceiver 302 (FIG. 3), which demodulates the signaland generates the received Log-likelihood ratios (LLRs) for a given TB.The HARQ combining element 1408 combines the received LLRs with storedLLRs for the TB from a previous transmission. The combined LLRs aredecoded by the processor 304 at block 1410 and may be passed to anotherprocess (e.g., sent to higher layers for further processing). If the TBis not successfully decoded, then the combined LLRs for that TB arestored in a partition 314 of a soft buffer 1412.

If a TB is not successfully decoded at block 1410, the UE may transmitthe HARQ feedback on its uplink. The soft buffer 1412 holds the combinedLLRs for a TB until the UE makes another attempt to decode the TB.

The transmitting entity (not shown in FIG. 14), upon receiving the HARQfeedback indicating the UE has not successfully received the TB,attempts to retransmit the TB. The retransmitted TB is put through thesame functional blocks as before, but when the UE attempts to decode theretransmitted TB at block 1410, the UE retrieves the LLRs for the TBfrom its memory 1414, and uses the HARQ combining element 1408 tocombine the received LLRs and the stored LLRs for the TB in a processknown as “soft combining.” The combined LLRs are provided to the decoder1410, which decodes the TB and provides the successfully decoded TB tohigher layers for further processing.

The soft buffer 1412 may also be referred to as a HARQ memory or HARQbuffer. Since there are multiple HARQ processes, a HARQ process index orHARQ identity (typically signaled using an explicit field within DCIformat associated with the TB (e.g. for downlink), or implicitlydetermined via subframe number, system frame number, etc (e.g. foruplink)) is made available for the HARQ combining element 1418 tocorrectly perform the combining operation. For the uplink transmission,the implicit HARQ process index is used by the UE to correctly determinethe coded bits for uplink transmissions.

If UE is configured with a transmission mode with a maximum of one TBper HARQ process (or one TB per TTI), the soft buffer of the UE may bedivided into eight partitions 1414 as shown in FIG. 14. If the UE isconfigured with transmissions modes with a maximum of two TBs per HARQprocess (or two TBs per TTI), each of the eight partitions 1414 may befurther divided into a first partition 1414A and a second partition1414B or the soft buffer of the UE may be divided into sixteenpartitions.

In an LTE embodiment of the invention, a UE's soft buffer configurationis determined at least in part by its category. Referring to Table 1,for example, a UE of Category-3 is expected to offer 1,237,248 softchannel locations, wherein each soft channel location can store aLog-likelihood ratio (LLR).

For FDD, for a given component carrier, a UE has eight HARQ processes inDL. Based on the transmission mode, the UE is capable of receiving oneor two transport blocks (corresponding to a HARQ process) within a TTI.Thus, a UE may determine the amount of storage per received transportblock based on the total number of soft channel bits, the maximum numberof HARQ processes, the transmission mode, etc. Similarly, NE1 may encodeand transmit only those coded bits that it knows the UE is capable ofprocessing and/or storing.

In some scenarios, if the UE has insufficient amount of storage for agiven transport block, and a decoding failure occurs, the UE may chooseto store some LLRs and discard some other LLRs. In other scenarios, ifno storage is available or no storage is deemed necessary for atransport block, if a decoding failure occurs, the UE may discard allLLRs corresponding to the transport block. Such scenarios typicallyoccur where the network entity transmits a quantity of coded bits thatexceed the storage capacity of the UE. Typical examples include: (1)when carrier aggregation is being used (e.g., a UE is supporting two ormore carriers, and 8 HARQ processes per carrier), and (2) When TDD isbeing used (e.g., UE supporting up to 15 HARQ processes per carrier).For FDD, and for uplink, for a given component carrier, a UE has eightHARQ processes when the UE is not configured in UL-MIMO transmissionmode (16 when the UE is configured in UL-MIMO transmission mode). ForTDD, the number of HARQ processes for the uplink is determined based onthe TDD UL/DL configuration.

With reference to Table 1, the soft buffer dimensioning for UE Category3 in LTE Rel-8/9 is defined assuming Limited Buffer Rate Matching(LBRM). With LBRM, for a subset of large TB sizes, the UE is allowed toprovision a per TB soft buffer size that is smaller than the maximumrequired soft buffer size to achieve mother code rate of ⅓. For example,a standard-compliant LTE Category 3 UE operating with 2 spatial layersshould support a largest TB size of 75376. For this TB size, given1237248 total soft channel bits (i.e., soft buffer size corresponding tothese bits), the UE can only provision 77328 soft channel bits per eachof the two possible TBs within a TTI. This amounts to an effectivemother code rate (ECR) or minimum achievable code rate of around 0.97for that TB size. The effective mother code rate may be defined as thenumber of information bits divided by the number of encoded bits thatcan be stored in the soft buffer

It is to be noted that the effective mother code rate may be differentfrom the code rate employed by the FEC encoder (e.g. turbo code), as thetwo are defined from different perspectives. It is possible to have aturbo code (FEC encoder) code rate of ⅓, wherein the code is shortenedor some of the output parity bits are punctured (due to soft bufferstorage limitations) to lead to an effective mother code rate largerthan ⅓. For example, if 50% of the output parity bits are punctured,then the ECR is approximately ⅔ whereas the turbo code rate is ⅓. For TBsizes less than 25456 approximately, the ECR is the same as mother coderate of ⅓, which means that LBRM need not be employed.

In an LTE embodiment of the invention, the number of soft channel bitsfor encoding a TB is determined as follows:

$N_{IR} = \left\lfloor \frac{N_{soft}}{K_{C} \cdot K_{MIMO} \cdot {\min \left( {M_{{DL}\; \_ \; {HARQ}},M_{limit}} \right)}} \right\rfloor$

where N_(soft) is the total number of soft channel bits, K_(MIMO) isequal to 2 if the UE is configured to receive PDSCH transmissions basedon spatial multiplexing with rank greater than 1 such as transmissionmodes 3, 4 or 8, 1 otherwise, M_(DL) _(—) _(HARQ) is the maximum numberof DL HARQ processes (i.e., HARQ processes in the downlink direction),and M_(limit) is a constant equal to 8, K_(C) is a value (from 1, 2 or5) dependent on the UE category and UE capability with regard to supportof a number of spatial layers for the component carrier on which thetransport block is transmitted. If a UE signals a Rel-10 UE category(one of 6, 7, 8) it also signals a corresponding second category (one of4, 5) for backward-compatibility (e.g. to allow a Rel-10 Category6 UEoperate in a Rel-8/9 network). The value of N_(soft) used for encoding aTB is based on the signaled UE category, maximum number of layerssupported by the UE on the particular component carrier, etc. On the UEside, the number of soft channel bits that UE offers for storing a TB ona carrier may be given by the same formula above, but replacing N_(soft)with N_(soft)/N_(cell), where N_(cell) is the number of configuredcomponent carriers for the UE.

When the UE transmits a transport block on the uplink to a networkentity, LBRM is typically not applied because the network entity hasadequate memory resources. Therefore, for uplink transmission, thenumber of encoded bits for a transport block is given by the turbo codemother code rate with the LBRM being transparent. This implies that therate-matching procedure on the downlink direction (with LBRM) and thesame in uplink direction (i.e. w/o LBRM) is not symmetric.

D2D Communication

In an embodiment of the invention, UEs engage in D2D communication usingresources of either the UL or the DL carriers. The UEs may also engagein D2D communication using resources of other carriers that are not usedby the UEs to communicate with the network entities.

The UEs may, in an embodiment of the invention, engage in D2Dcommunication with one another on a frame structure that usestime-frequency resources of either the UL carrier or the DL carrier. Insome embodiments the structure of the frame is based on a TDD frame. TheD2D frames/subframes can be completely distinct from theframes/subframes that are used by the UEs to communicate with thenetwork elements.

In various embodiments of the invention, UEs transmit data to oneanother over channels defined similar to PUSCH when the UEs are engagedin D2D communication, such as D2D-SCH (D2D-Shared Channel) or PUCCH-D2D.The PUCCH-D2D may be seen as another instantiation of a configuredD2D-shared channel.

The RBs of an RB pair assigned for a D2D link may be next to one anotherin the subframe or may be separated in frequency. In some cases, whenthe UEs are engaged in D2D communication, the UEs transmit data to oneanother over a separate physical channel that is defined specificallyfor D2D communication (e.g., D2D-SCH).

The RBs of an RB pair assigned for a D2D-SCH may be next to one anotherin the subframe or may be separated in frequency. The RBs of an RB pairassigned for a D2D-SCH may be next to RBs of an RB-pair assigned forPUSCH. RBs assigned for PUSCH and RBs assigned for D2D-SCH may share thesame UL carrier. D2D links carrying user data and control informationbetween UEs can occur over D2D-SCH or similarly defined links. Theconfiguration for the D2D links may be similar to PUSCH, PDSCH or PUCCH.The PDSCH may be appropriate since one UE is transmitting to another,similar to the network transmitting to a UE in regular cellularcommunications.

Determining Whether D2D Communication is to be Used

In accordance with an embodiment of the invention, UEs enter D2D modebased on a decision making process. This decision making process may becarried out by one or more of the UEs, and/or by a network entity. A UEor network entity can make this determination when the UE is in idlemode, in which the UE is generally not communicating with the network100, except for sending or receiving location information, pagingsignals, and emergency signals. The UE or network entity can also makethis determination when the UE is in a connected mode, in which thenetwork 100 has obtained information about the specific UE, andmaintains that information.

Once it has been decided that the UEs are to start communicating withone another in D2D mode, either one or more of the UEs requestspermission to begin D2D communication from the network entity, or thenetwork entity orders, without receiving a request, one or more of theUEs to enter D2D mode. In an embodiment of the invention, the decisionis made by, at least in part, by the core 106. It is to be understood,however, that the decision of whether or not the UEs can enter D2Dcommunication (e.g., a command to do so) is communicated to the UEs fromthe network entity, even if the resources of the core 106 take part inthe decision making.

According to an embodiment of the invention, the determination as towhether or not UEs should communicate using D2D is made based on one ormore of a variety of factors, including the proximity of the UEs to oneanother, the strength of reference signals that one of the UEs receivesfrom the other UE, the strength of the signals that the network entityreceives from one or more of the UEs, the detection of a user input.

In one embodiment, the UE or network entity makes the D2D determinationbased on the strength of a public safety network signal (e.g., a publicsafety UE reference signal) that a UE and/or network entity detects. Asa result of the detected strength, it may be decided that the UEs willreduce their maximum transmit power, or that they will refrain from D2Dcommunication entirely. For example, if the public safety network signalis weak, then the UEs or network entity may decide to refrain from D2Dcommunication. If the public safety network signal is strong, then theUEs or network entity may decide to proceed with D2D communication.However, in an emergency (e.g., a UE dials 911) a UE may be permitted totransmit critical information, such as its location, in D2D mode. Insuch a case, the UE would be able to use a limited, designated set ofresources (subframes and/or resource blocks) to communicate.

In an embodiment of the invention, a network entity determines whetherto set up a D2D connection between UEs based on the ability of each UEto engage in D2D communication, and based on the ability of each UE toengage simultaneously in both D2D and regular cellular communication.The network entity may, prior to making this determination, establish aconnection with one or more of the UEs. In such case, the D2Dcommunication may occur on the same carrier that the network entity usedfor connecting to the UEs.

Referring to FIG. 1, the network entities and the UEs may request andreceive information from the core 106 to assist in making the D2Ddetermination. A network entity can determine the proximity between theUEs by requesting location information from the core (which may maintaina record of the location of the UEs and/or subscription information) orusing GPS location reports from the UEs. The network entity candetermine the strength of signals that, for example, UE2 receives fromUE1 by obtaining a report from UE2 describing the strength of referencesignals transmitted by UE1. The UEs can also determine their proximityto one another using the DM-RS configuration of the other UE sent out bynetwork entity. The DM-RS serve as reference signals that are used bythe UE in conjunction with a threshold to determine their proximity toone another.

In some circumstances, UEs may be operating in different cells, yet beclose enough and have a strong enough signal between them to communicateD2D. For example, in FIG. 1, UE2 and UE3 may be able to communicateusing D2D even though UE1 is in C1 and UE3 is in C2. In such a case, thenetwork entity of C1 may need to communicate with the network entity ofC2 via the backhaul network to coordinate the set of up such D2Dcommunication.

Reference Signals for Discovery

According to an embodiment of the invention, UEs having D2D capabilitycan transmit reference signals to allow other D2D-capable UEs todiscover them. There are many types of signals that a UE can use as areference signal for the purpose of D2D discovery. In an embodiment ofthe invention, a UE implements a D2D discovery reference signal bytransmitting a zero power PUSCH or PDSCH, in which only the embeddedDM-RS has a non-zero power level. Alternatively, the UE uses SRS, SR,HARQ feedback information as reference signals. Alternatively, the UEmay transmit a beacon signal specifically defined for D2D discovery. Thebeacon signal specifically defined for D2D discovery may be mapped tothe same RE locations in time-frequency that the UE would have used fortransmitting UL DM-RS or SRS to the network entity.

The reference signal may also include substantive data. For example, aUE can use an SR or HARQ feedback information as a reference signal. AnSR and HARQ feedback each have a one-bit field, which the UE can use toindicate information about itself, such as its receiver typecapabilities, power control information, mobility information (e.g., isthe device stationary), or information about its preferred/desired D2Doperating mode to be used for communication.

In one embodiment of the invention, the network entity over-provisionsan existing channel in order to provide resource blocks for use by theUEs to transmit a reference signal. In this embodiment, a UE transmits areference signal on resource blocks that are on or near the edge of thetransmission bandwidth configuration of a carrier. The transmissionbandwidth configuration contains resources blocks that the networkentity has configured for use for typical UE to network communication.Not all of the resource blocks within the transmission bandwidthconfiguration are necessarily used during a given time. Examples areshown in FIGS. 7A and 7B.

In another embodiment of the invention, the network entity definesadditional resource blocks on which UEs can transmit a reference signal.These additionally-defined resource blocks are within the channelbandwidth of the carrier, but are outside of the transmission bandwidthconfiguration. These resource blocks are on frequencies near theboundary of the spectral emissions mask. In some cases, transmissions onthese frequencies are of lower energy than those frequencies that arewithin the channel bandwidth. Examples are shown in FIGS. 7A and 7B.

There are many ways that the UEs may use a reference signal to determinewhether D2D communication is feasible. In one embodiment, a UE variesthe power level of the reference signal using a ramping scheme. Forexample, referring to FIG. 8A, UE1 transmits a reference signal. UE1varies increases the energy of the reference signal over successive,adjacent symbols/subframes. UE2 receives the reference signal, andmeasures the energy per symbol or per subframe of the reference signal.UE2 then determines whether the energy it detects in the referencesignal reaches at least a predetermined level (e.g., predeterminedaccording to a communication standard used by UE1 and UE2). UE2 thenmakes the D2D feasibility determination based on the reference signalenergy detected. If the reference signal energy detected by UE2 does notreach the predetermined level, then UE2 does not initiate D2Dcommunication. If the detected energy level does reach the threshold,UE2 initiates D2D communication. Alternatively, UE2 reports, to thenetwork entity, the highest reference signal power level that UE2 canreceive, and the network entity determines whether D2D communicationshould occur, and orders one or both of the UEs to engage in D2Dcommunication.

In another embodiment, reference signals may be transmitted at apredetermined power level. The predetermined power level may be lowerthan the maximum power level allowed for D2D. The predetermined powerlevel may be a power level known to all UEs in a cell and may bedetermined based on a signal received from a network entity associatedwith the cell. For example, the network entity broadcasts the allowedreference signal power level for D2D communication for all UEs served inthat cell. This effectively allows the network entity to control therange of D2D communication between UEs attached to that serving cell.

In another embodiment, UEs in a serving cell communicating with thenetwork entity using a particular RAT, can report measurements or otherinformation relevant to another RAT to the network entity, and thenetwork entity can use this information determine the proximity of theUEs. For example, the UEs may report the service set identifiers (SSIDs)or other Medium Access Control IDs (MAC IDs) of the wireless accesspoints that are ‘visible’ to them (for example signal strength or otherrelated measurement such as RSRP or RSRQ or RSSI exceeds a threshold) tothe network entity, and if the base station determines that two UEs cansee the same access point (i.e., two UEs report same SSID or MAC ID), itcan then configure the devices to turn on their D2D reference signals.More generally, UEs may report the small cell identifiers of the smallcells that are ‘visible’ to them to the network entity, and if the basestation determines that two UEs can see the same small cell, it can thenconfigure the devices to turn on their D2D reference signals.

Frame/Subframe Format

According to an embodiment of the invention, UE1 and UE2 communicatewith one another using the frame format shown in FIG. 8B. The subframesare time-multiplexed, with UE1 and UE2 transmitting on differentsubframes. An exception is during a special subframe, during which afirst set of symbols of the subframe is reserved for UE1 to transmit; asecond set of symbols is a guard interval during which neither UEtransmits to the other; and a third set of symbols is reserved for theother UE to transmit. In some embodiments, one or more of the subframesare reserved for use by one or more of the UEs to listen for downlinkdata from a network entity.

In an embodiment of the invention, the UE1 and UE2 (FIG. 1) communicatewith one another using the general frame structure of FIG. 8B. As shown,the frame 800 includes regular subframes #0, #2, #3, #4, #5, #7, #8, and#9. Each of the regular subframes will be used for D2D, or forcommunicating with the network entity. Subframes #1 and #6, which arelabeled with reference numbers 801 and 803, are special subframes. Aspecial subframe provides a transition, in which a UE1 (but not UE2)transmits during a first set of symbols 802, the second set of symbols804 are used as a guard interval, in which neither the UE1 nor UE2transmits using those resources, and a third set of symbols 806, inwhich UE2 (but not UE1) transmits.

In an embodiment of the invention, the UEs can switch their order oftransmission in another special subframe 803, in which UE2 (but not theUE1) transmits during a first set of symbols 808, the second set ofsymbols 810 are used as a guard interval, in which neither the UE1 norUE2 transmits using those resources, and a third set of symbols 812, inwhich UE1 (but not UE2) transmits. This scheme will be described in moredetail with the examples that follow. The placement of the specialsubframes in FIG. 8B is meant for illustration purposes only, and theexamples below may have them placed differently.

Reference will now be made to FIGS. 9, 10, and 11 in order to describehow D2D communication occurs in different embodiments of the invention.It to be understood that special subframes may be implemented using thestructure of the special subframes 801 and 803 of FIG. 8B. It is also tobe understood that some embodiments, the entire special subframe is aguard interval, while in other embodiments, the guard interval lasts foronly a single symbol.

Referring to FIG. 9, it will be assumed that UE1 is sending a file toUE2, and UE1 has been allocated three subframes for every one subframeallocated to UE 1. Further, it will be assumed that the data beingtransferred is organized into blocks of data, such as transport blocks,packets, bursts, or the like. In subframes 900, 910, 920, and 930, UE1transmits the first block 912 to UE2. UE1 and UE2 switch transmitter andreceiver roles during the special subframe of slot 940. In subframe 950,UE2 transmits to UE1 (e.g. data and/or control information, such as anACK). Again, UE1 and UE2 switch roles during special subframe 960. UE1transmits a second block 914 to UE2 during subframes 970, 980, and 990.

Referring to FIG. 10, another embodiment is shown. In this embodiment,UE1 and UE2 communicate on time-duplexed slots. In slots 1000, 1010,1020, and 1030, UE1 transmits block 1012 to UE2. In slot 1040, there isa special subframe, configured as the subframes 801 and 803 shown inFIG. 8B. UE1 and UE2 switch transmitter and receiver roles during thespecial subframe of slot 1040. UE1 then transmits a second block 1014 toUE2 during slots 1050, 1060, 1010, and 1080. In a slot 1090, whichincludes a special subframe, UE1 and UE2 switch roles, with UE2 becomingthe transmitter, and UE1 becoming the receiver.

Referring to FIG. 11, another embodiment is shown. In this embodiment, asubframe is set aside to allow UE1 and UE2 to receive signals (such aspaging messages) from the network entity NE1. In the illustratedexample, UE2 transmits on subframes 1110, 1120; UE1 transmits onsubframes 1140 (which includes a one symbol gap at the beginning), 1150,1160, 1170, and 1180; and UE2 transmits on subframe 1190, which includesa one symbol gap at the beginning. On subframe 1100, both UE1 and UE2listen for signals from NE1. UE1 and UE2 may listen to NE1 on a regularbasis, such as during each subframe following the transition subframe.

Network-Initiated D2D Communication

Referring again to FIG. 8A, in an embodiment of the invention, thenetwork entity initiates D2D communication by allocating the appropriatetime-frequency resources to the UEs, which the UEs can use tocommunicate with one another, signaling information about the allocatedresources to the UEs, and ordering the UEs to communicate directly withone another using the allocated resources. One or both of the UEs may bein idle mode at the time the D2D communication is initiated, but arealready camped, so that they are known to network entity.

The time-frequency resources allocated to the UEs may be a subset of theUL resources, or may be a subset of the DL resources. For example, thenetwork entity may allocate one or more resource blocks of a UL subframeor a DL subframe. These allocated resource blocks may occurperiodically, such as every frame, subframe, or slot. Using theseallocated RBs, UE1 and UE2 create a data stream, which, for example, isstructured as a series of time-multiplexed subframes or slots, in whicheach subframe or slot uses one RB of the UL carrier or the DL carrier.The RBs of the UL or DL carriers that the UEs use may be on anysubcarrier of the UL or DL carrier. In certain embodiments, however, theRBs used by the UEs are taken from the UL carrier. These RBs areselected from the PUCCH of the UL carrier and are thus located at thehighest and lowest frequency subcarriers of the UL carrier.

Referring still to FIG. 8A, the carrier from which a resource isallocated for UE1 and UE2 D2D is a first carrier. The carrier that UE1or UE2 uses to communicate with the network entity is a second carrier.Furthermore, the UE1 and UE2 may communicate in D2D mode using a thirdcarrier that does not overlap with either the first or second carriers.

Referring to FIG. 12, an example of how D2D communication is initiatedby the network 100 will now be described. As noted in the figure, the ULcarrier is designated as the first carrier, while the DL carrier isdesignated as the second carrier. At step 1200, UE1 establishescommunication with NE1. This step may have been performed long beforethe remaining steps (e.g., via RACH). At step 1201, NE1 determines,based on one or more of the criteria set forth above, whether D2Dcommunication between UE1 and UE2 is needed or desirable.

If NE1 determines that D2D is needed or desirable, then, at step 1202,NE1 orders UE1 to turn on its reference signal. If UE2 is connected toNE1, then, at step 1204, NE1 requests information from UE2 regarding thelink quality of the reference signal as measured by UE2.

If it happened that UE2 was not connected to NE1, then NE1 couldrequest, via the backhaul system and core 106, that UE2 connect withNE1. The core 106 may enable this by paging UE2 via another networkelement, such as NE2. In response to the page, UE2 would then initiate aconnection to NE1.

At step 1206, UE2 determines the link quality and reports the linkquality (e.g., RSRP, RSRQ, RSSI, CSI) to NE1. At step 1208, NE1determines whether certain D2D criteria are met, such as whether (a) UE1and UE2 are within a predetermined distance of one another, (b) thequality of the reference signal received by UE2 from UE1 is above apredetermined level, and (c) allowing UE1 and UE2 would not adverselyimpact public safety communications.

If NE1 makes positive determinations regarding these factors, then theprocess continues at step 1210, at which NE1 allocates resources for D2D(e.g., allocates PUCCH resource blocks). If NE1 makes negativedeterminations about any of these factors, then NE1 does not initiateD2D mode for the UEs.

At steps 1211A and 1211B, NE1 transmits a command to UE1 and UE2. Thecommand orders the UEs to communicate with one another using D2D, andidentifies to them the RBs that they should use. NE1 may transmit thecommand to the UEs on, for example, the PDSCH or the PDCCH/EPDCCH. Atstep 1212, the UEs may engage in a handshaking procedure via theresources allocated by NE1. At step 1214, the UEs communicate with eachother in D2D mode. It should be noted steps 1210 and step 1211A (or1211B) may be performed as a single step. It should also be noted thatthe UEs may, in various embodiments, communicate on the UL carrier, DLcarrier, or a third, separate carrier.

Device-Initiated D2D Communication

In a device-initiated scheme, one or more of the UEs transmits a requestto network. The request includes the identity of another UE with whichthe requesting UE wishes to communicate. If the network grants therequest, the network responds by allocating the appropriate resourcesand configuring the UEs to use those resources.

For example, assume that users of UE1 and UE2 are aware of one another(e.g., they are next to each other, have discovered each other using a“finding friends” application such as Google Latitude™ or near fieldcommunication (NFC)). The user of UE1 decides to transfer a file to theuser of UE2. If both UEs are not already on the network, UE1 should beable to request that UE2 be connected to UE1's network or to a commonnetwork. UE1 and UE2 can then operate on the same band/carrier, and beallocated resources from the network on which they are operating asdescribed above.

In an embodiment of the invention, if the UEs are in idle mode then UE1may enter a connected mode by connecting to NE1 and indicating “D2Dinterest” to NE1. UE1 may provide information about UE2 to NE1. Suchinformation may include the IMEI of UE2, or handle-like information suchas UE2's userid@network_name.d2d, or the like. The network entity passesthis information on to the core 106 (e.g., to a billing server) (FIG.1). One or more of the control elements checks the subscriptioninformation for both of the UEs to determine whether the data plans forthe UEs include D2D capability. The core then provides a success orfailure indication to NE1.

NE1 may obtain updated mobility measurements for each UE, and provideupdated mobility measurements to the UEs, thereby allowing NE1 tocontrol measurements and mobility.

In one implementation of the device initiated D2D, UE1 (in idle mode)determines that it can carry out D2D communication with UE2, usingspectrum in a particular frequency band. UE1 then connects to a networkentity operating in that frequency band and downloads, from the network100, information that can be used for D2D communication, such asreference signal power, reference signal identifying information,maximum power allowed for D2D communication and other power controlparameters, and the subframes that the network 100 allows UE1 to use forD2D communication. UE1 then initiates D2D (e.g., by starting to transmita reference signal). UE2 performs similar steps and also initiates D2D.The UEs can release their connection to the network (i.e., move back toidle mode) after downloading the D2D information, and continue tocommunicate in a D2D mode, even though they are in idle mode withrespect to the network 100. For this implementation, the network 100 mayalso indicate a “validity duration” associated with the informationrelated to D2D transmission. Alternately, a predefined validity periodmay be assumed the UEs, and if the duration of the D2D session exceedsthe validity period, the UEs may need to re-connect to the network tocheck if the D2D information is still valid or if they have to downloadnew values.

The handover of a UE from NE1 to another may be delayed until after theD2D session between the UEs is complete.

According to an embodiment of the invention, UE1, upon determining thatD2D may be used, autonomously initiates D2D communication in a set ofuplink RBs in a frequency band containing the uplink carrier. The UE1can determine the set of uplink RBs based on signaling received fromNE1. NE1 can refrain from scheduling regular UE transmission (i.e., UEto network entity transmission) in those RBs. If NE1 does this, the UEsin D2D mode may be able to communicate with maximum power possible forD2D communication. This is useful for example, when the UE is used in apublic safety scenario. For example, if the public safety UE determinesthat it is out of coverage from an LTE network for infrastructure basedcommunication, it can autonomously fall back to D2D mode over a set ofpotentially pre-determined uplink RBs.

Referring to FIG. 13, an example of device initiated D2D communicationwill now be described. At step 1300, a user interacts with the userinterface of UE1 to indicate the user's desire to engage in D2Dcommunication. At step 1302, UE1 transmits, via a first carrier or ULcarrier, a request to NE1 for D2D communication with UE2. At step 1304,NE1 determines whether UE2 is connected. If it is not, then NE1requests, to the core 106, that UE2 be connected to NE1. If UE2 isalready connected, or becomes connected in response to the request fromNE1, then NE1 allocates resources (e.g., RBs from the UL carrier or theDL carrier) for use by the UEs for the D2D communication. At steps 1306Aand 1306B, NE1 transmits, via a second carrier or DL carrier,information identifying the allocated resources to the UEs. At step1308, the UEs can carry out a handshaking procedure using the allocatedresources, and using a D2D subframe structure. At step 1310, the UEscommunicate with one another using the D2D subframes.

UE Capabilities and Capability Partitioning

According to an embodiment of the invention, each UE has a set of one ormore capabilities, i.e., a capability configuration. A capabilityconfiguration may include one or more of:

-   -   (1) the data rate (e.g., the maximum data rate) that a UE        supports;    -   (2) how many transmit and/or receive antennas the UE has;    -   (3) the types of transmission schemes supported by the UE        (Tables 3 and 4 show examples of transmission schemes);    -   (4) the soft buffer configuration of the UE;    -   (5) the UE's MIMO capability (e.g., supported number of layers        per band, support of UL MIMO);    -   (6) the UE's the carrier aggregation capability    -   (7) the UE's battery life;    -   (8) the maximum number of transport block bits rate per TTI        supported by the UE    -   (9) the UE's processing capability (e.g., the number of        processors a UE has, the number of simultaneous processes it can        execute at one time).

Each UE may, in an embodiment of the invention, divide its capabilities.Each divided set of capabilities will be referred to as a capabilitypartitioning configuration.

As noted, one of the capabilities that a UE can partition is its softbuffer configuration. A UE's soft buffer configuration is one or more of(1) the maximum number of HARQ processes that the UE will use forreceiving packets (the number of buffer partitions needed); (2) the sizeof a soft buffer that the UE will use for receiving packets; and (3) thenumber of soft channel bits that the UE will use for receiving packets.Thus, a first set of one or more of these characteristics wouldconstitute a first soft buffer configuration, and a second set wouldconstitute a second soft buffer configuration.

For example, given a first UE and a second UE, a first bufferpartitioning configuration may include at least one of: (1) a maximumnumber of HARQ processes that the first UE will use for receiving fromthe network entity; (2) the size of a soft buffer that the first UE willuse for receiving from the network entity, and (3) a number of softchannel bits that the first UE will use for receiving from the networkentity.

The second buffer partitioning configuration comprises at least oneof: 1) a maximum number of HARQ processes that the first UE will use forreceiving from the second UE; 2) the size of a soft buffer that thefirst UE will use for receiving from the second UE, and 3) a number ofsoft channel bits that the first UE will use for receiving from thesecond UE.

An example of a UE dividing its capabilities into capabilitypartitioning configurations will now be provided. If a UE has twoprocessors and two antennas, it could divide these capabilities into afirst capability partitioning configuration, which constitutes oneprocessor and one antenna, and a second capability partitioningconfiguration, which constitutes one processor and one antenna.

In an embodiment of the invention, a UE uses different capabilitypartitioning configurations for communicating with different devices.For example, a UE might communicate with a network entity using a firstcapability partitioning configuration of 1 processor, 4 soft bufferpartitions, and in transmission mode 1. The UE might also communicatewith another UE in D2D mode using a second capability partitioningconfiguration of 1 processor, 2 soft buffer partitions, and in D2Dtransmission mode. This example also illustrates a UE changing its softbuffer configuration. The first soft buffer configuration would include4 soft buffer partitions and the second soft buffer configuration wouldinclude 2 soft buffer partitions.

In some embodiments, the UE communicates with two other devices, such asanother UE and a network entity, simultaneously using both a first and asecond capability partitioning configuration. In other embodiments, theUE switches from using one capability partitioning configuration toanother depending on the device with which the UE is communicating, anddo so in a time-multiplexed manner.

Any of the capability configurations of a UE, including those made up ofone or more of the capabilities noted above, may be divided intomultiple capability partitioning configurations.

Referring to FIG. 1, for example, UE1 may change its capabilitypartitioning configuration (e.g., lower its data rate, alter number ofsoft buffer partitions, etc.) so that its configuration is compatiblewith that of UE2 so at to allow UE1 and UE2 to communicate with oneanother, while also supporting communication between UE1 and the networkentity. UE2 may also change its capability partitioning configuration sothat the capability partitioning configuration of UE1 and theconfiguration of UE2 are compatible.

For example, if UE1 can transmit up to 100 megabits per second, and UE2can receive up to only 50 megabits per seconds, then UE1 may change itscapability configuration so that it only transmits up to 50 megabits persecond.

An example of different LTE UE categories/capabilities that UEs may havein an embodiment of the invention is shown in Table 1 (for the downlink)and Table 2 (for the uplink).

TABLE 1 Downlink physical layer parameter values set by the fieldue-Category Maximum Maximum number number of of bits Maximum DL-SCH of aDL- number of transport SCH Total supported block transport number oflayers bits received block soft for spatial within a TTI receivedchannel multiplexing UE Category (Note) within a TTI bits in DL Category1 10296 10296 250368 1 Category 2 51024 51024 1237248 2 Category 3102048 75376 1237248 2 Category 4 150752 75376 1827072 2 Category 5299552 149776 3667200 4 Category 6 301504 149776 (4 layers) 3654144 2 or4  75376 (2 layers) Category 7 301504 149776 (4 layers) 3654144 2 or 4 75376 (2 layers) Category 8 2998560 299856 35982720 8

TABLE 2 Uplink physical layer parameter values set by the fieldue-Category Maximum number Maximum number of of bits of an UL- UL-SCHtransport SCH transport Support for block bits transmitted blocktransmitted 64QAM UE Category within a TTI within a TTI in UL Category 15160 5160 No Category 2 25456 25456 No Category 3 51024 51024 NoCategory 4 51024 51024 No Category 5 75376 75376 Yes Category 6 5102451024 No Category 7 102048 51024 No Category 8 1497760 149776 Yes

TABLE 3 PDCCH/EPDCCH and PDSCH configured by C-RNTI TransmissionTransmission scheme of PDSCH mode DCI format Search Space correspondingto PDCCH Mode 1 DCI format 1A Common and Single-antenna port, port UEspecific by C-RNTI DCI format 1 UE specific by C-RNTI Single-antennaport, port 0 Mode 2 DCI format 1A Common and Transmit diversity UEspecific by C-RNTI DCI format 1 UE specific by C-RNTI Transmit diversityMode 3 DCI format 1A Common and Transmit diversity UE specific by C-RNTIDCI format 2A UE specific by C-RNTI Large delay CDD or Transmitdiversity Mode 4 DCI format 1A Common and Transmit diversity UE specificby C-RNTI DCI format 2 UE specific by C-RNTI Closed-loop spatialmultiplexing or Transmit diversity Mode 5 DCI format 1A Common andTransmit diversity UE specific by C-RNTI DCI format 1D UE specific byC-RNTI Multi-user MIMO Mode 6 DCI format 1A Common and Transmitdiversity UE specific by C-RNTI DCI format 1B UE specific by C-RNTIClosed-loop spatial multiplexing using a single transmission layer Mode7 DCI format 1A Common and If the number of PBCH antenna ports UEspecific by C-RNTI is one, Single-antenna port, port 0 is used,otherwise Transmit diversity DCI format 1 UE specific by C-RNTISingle-antenna port, port 5 Mode 8 DCI format 1A Common and If thenumber of PBCH antenna ports UE specific by C-RNTI is one,Single-antenna port, port 0 is used, otherwise Transmit diversity DCIformat 2B UE specific by C-RNTI Dual layer transmission, port 7 and 8 orsingle-antenna port, port 7 or 8 Mode 9 DCI format 1A Common andNon-MBSFN subframe: If the number UE specific by C-RNTI of PBCH antennaports is one, Single- antenna port, port 0 is used otherwise Transmitdiversity MBSFN subframe: Single-antenna port, port 7 DCI format 2C UEspecific by C-RNTI Up to 8 layer transmission, ports 7-14 orsingle-antenna port, port 7 or 8 Mode 10 DCI Format 1A Common andNon-MBSFN subframe: If the number UE specific by C-RNTI of PBCH antennaports is one, Single- antenna port, port 0 is used otherwise Transmitdiversity MBSFN subframe: Single-antenna port, port 7 DCI format 2C UEspecific by C-RNTI Up to 8 layer transmission, ports 7-14

The content of Tables 1 and 2 can generally be found in “LTE; EvolvedUniversal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radioaccess capabilities (3GPP TS 36.306 version 10.0.0 Release 10)” (by 3rdGeneration Partnership Project (3GPP) in January 2011), Tables 4.1-1 and4.1-2.

The content of Table 3 can generally be found in “TechnicalSpecification Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA); Physical layer procedures” (Release 11), (3rdGeneration Partnership Project (3GPP), September 2012) Tables 7.1-5 and7.1-6. Table 3 shows the transmissions modes used for the downlink. A UEis configured in one of the transmission modes by the network entity. AUE in a given transmission mode monitors the downlink control channelsfor downlink control information (DCI) format corresponding to thetransmission mode and receives PDSCH based on the correspondingtransmission scheme (e.g. single antenna port, transmit diversity, openloop spatial multiplexing, closed loop spatial multiplexing, beam formedtransmission (single antenna port, port 7), etc).

Signaling Capabilities and Categories

According to an LTE embodiment, a UE informs a network entity of itsRelease, category, and additional capabilities. This allows the networkentity to properly configure its communication with the UE. A UE maydiscard (or disregard) any received message/signal that does not conformto its release/category/capabilities. A UE of a particular categoryoffers the characteristics/capabilities (in the downlink and uplink) asshown in Tables 1 and 2.

During their D2D handshake process, UEs may establish a master-slaverelationship. The UE having the best capability (e.g., the UE supportslarger data rate, longer battery life, etc.) will generally be themaster. For instance, if the two UEs participating in a D2D belong todistinct categories, then the UE with the larger category may be themaster device. For example if a Category 3 and a Category 7 deviceparticipate in D2D, then the Category 7 may be the master device. Themaster UE will dictate the resources that are expected from the slave UEfor the D2D communication. The slave UE may respond with a messageindicating that it cannot provide such resources. If this occurs, themaster UE may need to lower its expectations of the slave UE. Forexample, the slave UE may need to use at least some of its soft bufferpartitions to communicate with the network entity.

Capability Exchange Example

Referring to FIG. 15, an example of how UEs exchange capabilityinformation for the purpose of D2D communication will now be described.In the example, the following assumptions will be made. UE1 uses RBsfrom the UL carrier to transmit subframes to UE2 over a D2D carrier,using a structure such as that shown in FIG. 8B. UE1 in this example isa Category 4 UE and UE2 is a Category 2 UE. As shown in Tables 1 and 2,Category 4 UEs have DL/UL rates of 150 Mbps/50 Mbps, and Category 2 UEshave DL/UL rates of 50 Mbps/25 Mbps. Thus, the UE1-to-UE2 link has amaximum data rate of 50 Mbps (UE2-rx), and UE2-to-UE1 has a maximum datarate of 25 Mbps (UE2-tx). This asymmetry is in spite of the fact thatboth UEs have the capability to decode 50 Mbps.

It is also assumed that the network entity has already granted UE1authorization to engage in D2D communication with UE2, and that UE1 isaware of UE2 (UE2 may likewise be aware of UE1). These assumptions aremade for the purpose of illustration only.

At step 1500, UE1 establishes communication with NE1. At step 1501, NE1allocates RBs and/or subframes that the UEs may use to communicate withone another in D2D mode. These RBs may be RBs of the DL carrier or RBsof the UL carrier. At step 1510, UE1 determines a first set of theallocated RBs and/or subframes that the UEs will use to communicate withone another. At step 1520, UE1 receives information from NE1 regardingUE2's capabilities (e.g., UE2's category). Alternatively, at step 1520′,UE2 transmits its capability information to UE1 via the D2D carrier.

UE1 and UE2 then may initiate a handshake process with one another atstep 1530, in which they establish a master-slave relationship, agreeingthat UE1 is the master. At step 1540, UE1 determines the appropriateconfiguration for the UEs to enter for communication, including whatresources (e.g. capability) the UEs should allocated for D2Dcommunication. These include the data rate, coding scheme, and HARQbuffer configuration. In this example, UE1 determines that the UE2should devote three soft buffer partitions 1416 (in FIG. 14) forreceiving transport blocks from UE1. The UE2 may then, for example, usethe remaining five soft buffer partitions 1418 for communication withNE1. At step 1550, UE1 may inform the UE2 of the resources expected orthe UE1 may configure the required resources of UE2 for the D2Dcommunication. At step 1560, UE1 and UE2 communicate in D2D mode usingthe RBs/subframes allocated by NE1 in a D2D carrier, and using theinternal resources that UE1 determined should be used. At step 1560, UE1and UE2 engage in a D2D communication.

A modified version of the procedure of FIG. 15 is depicted in FIG. 16.In the procedure of FIG. 16, the user of UE1 initiates the D2Dcommunication at step 1600. At step 1602, there are three alternativesdepicted. NE1 may inform UE1 of UE2's capability, UE1 may receivecapability information directly from UE2, or UE1 and UE2 may exchangecapability information with one another. The remaining steps are similarto those of FIG. 15.

To further illustrate capability and category exchange during D2Dcommunication according to an embodiment, assume that UE1 and UE2 engagein D2D communication and that UE1 is aware of therelease/capability/category of UE2. UE1 will then configure the D2D linksuch that UE2 can properly transmit encoded messages to, and receiveencoded transmissions from UE1. If the UEs are different categories, UE1may choose its soft buffer configuration based on UE2's category. Thehigher category UE may be configured as the master in the D2Dconnection.

In another embodiment of the invention, a UE may directly signal itscategory to another UE when the UEs are engaged in D2D communication.Furthermore, a network entity or the master device may configure (a) thesoft buffer allocation for D2D reception in the first UE and/or the HARQbuffer allocation for D2D reception in the second UE, b) the maximumnumber of HARQ processes for D2D transmission from the first UE to thesecond UE and/or the maximum number of HARQ processes configured for D2Dtransmission from the second UE to the first UE. Additionally, thenetwork entity may configure one or more of the following restrictions:

-   -   a) Transmission mode restriction    -   b) Modulation restriction (limited to QPSK/16-QAM)    -   c) Bandwidth restriction (e.g. if UE1 and UE2 are operating on        different BWs, UE1 is regular UE and UE2 is MTC device with a        smaller Rx BW).

The network entity may signal a default configuration for the D2Dcommunication. The signaling of the default configuration may be acell-specific signaling or UE-specific signaling the defaultconfiguration for the direct communication may include: transmissionmode for direct transmission, transmission scheme for directtransmission, demodulation RS configuration, component carrier(s) fordirect communication etc. The network entity may override/re-configuresome or all default configuration parameters when direct communicationwith another UE is enabled. The configuration may be valid for thesession or used by the UE for direct communication with the other UE forcertain predefined time duration. The configuration information may bereset to the default configuration within the predefined time durationon receiving a specific signaling from the network entity, transition toRRC idle mode, handover etc.

Control Channel Over-Provisioning

Referring to FIG. 7A, an example of how RBs are allocated for use byreference signals according to an embodiment of the invention will nowbe described. This example will focus on those RBs near the first edge722 of the transmission bandwidth configuration. However, the same RBallocation scheme may also be applied to those RBs near the second edge724.

It will be assumed for this example that, without any RBs being reservedfor D2D, the network entity would ordinarily allocate RB0 and RB1 to UEsfor transmission on the PUCCH. To facilitate D2D communication, however,the network entity instead allocates RB1 and RB2 for the PUCCH andreserves RB0 for D2D reference signaling. The network entity NE1 would,in the D2D case, provide information (e.g., via higher layer signaling,such as RRC signaling) to the UEs regarding the signal configuration ofthe reference signal. However, the network entity allocating inresources does not necessarily have to provide the signal configurationinformation. A second network entity, such as NE2, could do so.

In this example, the reference signal's signal configuration is that RB1and RB2 are to be used for the PUCCH, and that RB0 is to be used by theUEs to transmit reference signals. This RB allocation scheme allows UEsthat do not have D2D capability to use the PUCCH as they always have,but using RB1 and RB2, while the D2D-capable UEs are able to use RB0 forreference signaling in addition to using the PUCCH. Also, in many cases,the transmission power used for D2D communication is expected to besmall and using the edge RBs for D2D helps in reducing interferenceoutside the channel bandwidth.

One way in which the network entity can notify a first UE about thesignal configuration of a second UE's reference signal is bytransmitting information regarding the modified PUCCH RB allocations tothe first UE. Such information can be in the form of a modified nRB-CQIvalue.

In an LTE embodiment, for example, nRB-CQI (or N_(RB) ⁽²⁾) may denotethe bandwidth in terms of resource blocks that are available for use byPUCCH formats 2/2a/2b transmission in each slot in a subframe. PUCCHformats 2/2a/2b may be used for transmitting periodic CSI reports. AnLTE UE could use the nRB-CQI value to determine the PUCCH resources itwill use for transmitting HARQ-ACK using PUCCH format 1/1a/1b. Morespecifically, the LTE UE would not transmit HARQ-ACK using PUCCH format1/1a/1b in the edge RBs identified by nRB-CQI value.

To allow D2D communication on the edge RBs of a transmission bandwidthconfiguration, the signal configuration information sent by the networkentity can indicate an additional RB offset (e.g. D2D-RB-offset) usingwhich D2D capable UEs can determine the edge RBs used for D2Dcommunication. For example, if RBs of a transmission bandwidthconfiguration are numbered RB0, RB1, RB2, RB3, RB4 . . . with RB0 beingclosest to the transmission bandwidth edge, the network entity cansignal a D2D-RB-offset value 2 and nRB-CQI value of 5. UEs that are notconfigured for D2D communication (and UEs that are not capable of D2Dcommunication) do not transmit HARQ-ACK in the first 5 RBs starting fromthe edge of the transmission bandwidth configuration (i.e., RB0 to RB4).UEs that are configured for D2D communication use the first 2RBs (i.e.,RB0 and RB1) for D2D communication. The other RBs (i.e., RB2, RB3, RB4)can be used for PUCCH formats 2/2a/2b transmission by all the UEs. Asseen from the example, over-provisioning the PUCCH resource value (i.e.,signaling a larger value of n_RB_CQI than that needed to support PUCCHformat 2/2a/2b transmissions) allows the network 100 to support D2Dcommunication in a manner that is transparent to UEs that are notcapable of supporting D2D communication. Such transparent operation mayimprove overall network efficiency, since UEs that supports D2Dcommunication can share a carrier with UEs that do not support D2Dcommunication.

In another example, it will be assumed that the carrier 700 is using achannel (e.g., channel 13) that is adjacent to a public safety channel(e.g., channel 14), and that the network entity is not permitted to useRB0, RB1 and RB2. Under these circumstances, the network entityallocates RB4 and RB5 for use by the UEs for PUCCH and allocates RB3 forD2D reference signaling.

In another embodiment of the invention, the network entity defines an RBwithin one or more of the first spectral emissions region 708 and thesecond spectral emissions region 710 (RBs 730 and 718). These regionsordinarily would not be used for data or control signaling due to limitson the power of signals in those regions (imposed by, for example, lawor industry agreement) for avoiding interference to adjacent channels.However, because reference signals for D2D discovery purposes do notnecessarily have to be as strong as regular control signals, the UEs mayuse those RBs for D2D reference signals. The interference caused by theD2D reference signals is expected to be quite small as long as thetransmit power of the signals is kept a sufficiently low level.

In another embodiment of the invention, the techniques described inconjunction with FIG. 7A can be applied to an aggregated carrier 750(FIG. 7B). Edge RBs 0 of the three component carriers 752, 754, and 756of carrier 750 is used for D2D reference signaling, and RBs 1 and 2 isused for the PUCCH. As noted in conjunction with FIG. 7A, one or moreRBs 760 may be defined within the spectral emissions mask for use by theUEs for D2D reference signaling.

In another embodiment a specific PUCCH resource index is defined toindicate which portion of the normal (e.g., Rel-8 LTE) control channelsavailable for a given PUCCH are instead reserved for D2D referencesignaling channels. Note the other normal control channels supported bya given PUCCH may be HARQ-ACK channels, SRS channels, SR channels, andChannel state information channels which include rank information andprecoding feedback and channel quality feedback channels. This indexcould be signaled (broadcast) by higher layer signaling using a RadioResource Control (RRC) message sent as part of a system informationblock. The PUCCH resource index or which of the D2D reference signalingchannels to use for a UE to perform D2D reference signaling on could bedetermined by a field in a broadcast scheduling grant. Such a broadcastscheduling grant might also indicate which unscheduled/unassignedresource blocks in a subframe are available for random access or D2Ddata transmission. Such a broadcast scheduling grant may also bereferred to as a contention grant. A hashing function based on user ID(e.g. such as IMSI, radio network terminal indicator) and/or subframe,slot, or radio frame index could also determine which D2D referencesignaling channel to use for transmitting a given D2D reference signal.If PUCCH resources for D2D reference signaling are only to be used inspecific subframes or slots in a radio frame or in specific radio framesthen a subframe, slot, and/or radio frame indicator is also signaledregarding D2D reference signaling resources. The PUCCH resource indexcan be identified using a Δ_(Shift) ^(PUCCH) value, a n_(PUCCH) ⁽²⁾value or a n_(PUCCH) ⁽²⁾. The PUCCH resource index can also beidentified using a “Scheduling Request (SR) resource” value or acombination of the SR resource value and one or more of the valuesdescribed above, all of which can be signaled by the network entity. Thecandidate set of radio resources used for D2D reference signaling may beconsidered common resources where one or more UEs may transmit on theresources simultaneously.

In some embodiments, configuration information regarding the referencesignals can be received by a UE, from a network entity, in a DL carrierwithin a downlink operating band of a frequency division duplex (FDD)mode operating band. Reference signals (from another UE) can be receivedby the UE in a UL carrier within an uplink operating band of the FDDmode operating band. While the reference signals are received in the ULcarrier of the FDD mode operating band, other data related to D2Dtransmission (e.g. application data of the other UE formatted forphysical layer transmission) can be received in a separate carrier. Theseparate carrier may in a different operating band. Alternately, theother data may be received in the UL carrier within the uplink operatingband of the FDD mode operating band. In some cases, the reference signalmay be transmitted by the UE in a separate carrier.

After receiving a reference signal from another UE (UE2), the UE (UE1)can determine the link quality between UE1 and UE2 by measuring thereference signal and using the configuration information related to thereference signal. To determine the link quality, the UE may measureReference Signal Received Power (RSRP), Reference Signal ReceivedQuality (RSRQ), or Received Signal Strength Indicator (RSSI), or aChannel State Information (CSI). The UE can report the measured linkquality to the network entity from which it has received the referencesignal configuration information. In some cases, the UE may report themeasured link quality to a different network entity. For example the UEmay receive reference signal configuration information from a firsttransmission point but later report link quality (of a D2D link betweenUE and UE2) to another transmission point.

Generally UE reception of reference signal and UE reporting of linkquality to the network entity occur in different subframes. For caseswhere the UE receives reference signals in a UL carrier of a FDD modeoperating band, the UE is only expected to receive the reference signalsin only those subframes where it is not scheduled to transmit on thesame UL carrier.

Configuration information related to reference signals can includeinformation identifying the subframes in which the UE is expected toreceive reference signals, information identifying the resource elementsin a subframe in which the UE is expected to receive reference signals,RB index of the RBs on which the UE can receive the reference signals,RB offset (e.g. D2D-RB-offset) of the RBs on which the UE can receivethe reference signals, information identifying a reference signalsequence index or a reference signal cyclic shift of a reference signalassociated with the reference signal.

In some embodiments, the UE may receive information regarding a maximumtransmission power limit for communication on the carrier on which theUE has to transmit reference signals and/or other D2D data. In someimplementations, the maximum transmission power limit can be aconfigured maximum UE output power PCMAX,c where c is the carrier index)for the carrier on which the UE transmits reference signal and/or D2Ddata. The UE may also receive information related to Maximum PowerReduction (MPR) associated with D2D reference signal or other D2D datatransmission. When the UE receives information related to MPR values, itcan reduce its configured maximum UE output power for D2D transmissionbased on the MPR value. The UE can adjust the power of its referencesignal and/or D2D transmissions such that power of those transmissionsdoes not exceed the configured maximum UE output power for D2Dtransmissions.

The UE may receive configuration information related to referencesignals from via broadcast signaling from a network entity while the UEis in idle mode. In LTE, when the UE is in idle mode, the UE performsprocedures related to RRC_IDLE state. In LTE, The broadcast signalingcan be included is a Master Information Block (MIB) or a Systeminformation Block (SIB).

There are many uses to which the D2D communication embodiments describedherein may be put. For example, a user having a smartphone could engagein D2D communication with a D2D-capable kiosk to download movies.

The terms, descriptions and figures used herein are set forth by way ofillustration only and are not meant as limitations.

For example, in the present disclosure, when two or more components are“electrically coupled,” they are linked such that electrical signalsfrom one component will reach the other component, even though there maybe intermediate components through which such signals may pass.

In another example, interactions between UE1, UE2 and/or NE1 are oftendescribed as occurring in a particular order. However, any suitablecommunication sequence may be used.

List of Acronyms

-   BS Base Station-   CA Carrier Aggregation-   CCE Control Channel Element-   CoMP Coordinated Multi-Point-   CP Cyclical Prefix-   CQI Channel Quality Indicator-   CRC Cyclic Redundancy Check-   C-RNTI Cell RNTI-   CRS Common Reference Signal-   CSI Channel State Information-   CSI-RS Channel State Information Reference Signal-   CSS Common Search Space-   D2D Device to Device-   D2D-SCH D2D Shared Channel-   DCI Downlink Control Information-   DL Downlink-   DL-SCH Downlink Shared Channel-   DM-RS Demodulation Reference Signal-   DFT-SOFDM Discrete Fourier Transform Spread OFDM-   eNB Evolved Node B-   EPBCH Enhanced Physical Broadcast Channel-   EPDCCH Enhanced Physical Downlink Control Channel-   EPRE Energy Per Resource Element-   E-UTRA Evolved UTRA-   FDD Frequency Division Duplex-   FFT Fast Fourier Transform-   GPS Global Positioning System-   HARQ Hybrid Automatic Repeat Request-   IMEI International Mobile station Equipment Identity-   LBRM Limited Buffer Rate Matching-   LTE Long-Term Evolution-   MAC Media Access Control-   MBSFN Multicast-Broadcast Single Frequency Network-   MCS Modulation and Coding Scheme-   MIB Master Information Block-   MIMO Multiple-Input Multiple-Output-   MU-MIMO Multi-User MIMO-   NFC Near Field Communication-   OFDMA Orthogonal Frequency Division Multiple Access-   P/S-SCH Primary/Secondary Synchronization Channel-   PBCH Primary Broadcast Control Channel-   PCID Physical Cell Identifier-   PDCCH Physical Downlink Control Channel-   PDCP Packet Data Convergence Protocol-   PDSCH Physical Downlink Shared Channel-   PHICH Physical Hybrid ARQ Channel-   PMI Precoding Matrix Indicators-   PRB Physical Resource Block-   P-RNTI Paging RNTI-   PRS Positioning Reference Signal-   PSS Primary Synchronization Signal-   PTI Precoder Type Indication-   PUCCH Physical Uplink Control Channel-   PUSCH Physical Uplink Shared Channel-   QAM Quadrature Amplitude Modulation-   QPSK Quadrature Phase Shift-Keying-   RACH Random Access Channel-   RAT Radio Access Technology-   RB Resource Block-   RE Resource Element-   REG Resource Element Group-   RF Radio Frequency-   RI Rank Indicator-   RNC Radio Network Controller-   RNTI Radio Network Temporary Identifier-   RRC Radio Resource Control-   RRH Remote Radio Head-   RS Reference Symbol-   RSRP Reference Signal Received Power-   RSRQ Reference Signal Received Quality-   RSSI Received Signal Strength Indicator-   SC-FDMA Single-Carrier Frequency Division Multiple Access-   SFN System Frame Number-   SIB System Information Block-   SI-RNTI System Information RNTI-   SPS Semi-Persistent Scheduling-   SR Scheduling Request-   S-RNTI Serving RNC RNTI-   SRS Sounding Reference Signal-   SSID Service Set Identifier-   SSS Secondary Synchronization Signal-   TDD Time Division Duplex-   tm Transmission Mode-   TP Transmission Point-   TTI Transmission Time Interval-   UE User Equipment-   UERS UE-specific Reference Symbol-   UL Uplink-   UL-SCH Uplink Shared Channel-   UMTS Universal Mobile Telecommunications System

1. A method in a first user equipment, the method comprising receiving,in a first carrier, information regarding a signal configuration from anetwork entity; receiving, in a second carrier, a reference signal froma second user equipment, the second carrier associated with atransmission bandwidth configuration and a channel bandwidth, whereinthe transmission bandwidth configuration of the second carrier iscontained within the channel bandwidth of the second carrier, whereinthe received reference signal is within the channel bandwidth of thesecond carrier and in proximity to an edge of the transmission bandwidthconfiguration of the second carrier, determining a link quality of thereceived reference signal based on the signal configuration; andreporting the determined link quality to a network entity via the secondcarrier.
 2. The method of claim 1, wherein the network entity is a firstnetwork entity, the method further comprising: receiving, in the firstcarrier, information regarding the signal configuration from a secondnetwork entity.
 3. The method of claim 1 receiving, in the firstcarrier, information regarding the signal configuration from the networkentity.
 4. The method of claim 1 wherein the signal configurationincludes information regarding a resource block of the second carrier,wherein the resource block is within the channel bandwidth of the secondcarrier and proximate to an edge of the transmission bandwidthconfiguration of the second carrier, the method further comprisingreceiving the reference signal from the second user equipment on theresource block.
 5. The method of claim 1, wherein the first carrier iswithin a downlink operating band of a frequency division duplex (FDD)mode operating band, and wherein the second carrier is within an uplinkoperating band of the FDD mode operating band.
 6. The method of claim 1,wherein reporting the link quality to the network element furthercomprises transmitting, within the channel bandwidth of the secondcarrier, a report regarding the link quality, wherein the reportincludes information regarding one or more of a Reference SignalReceived Power (RSRP), Reference Signal Received Quality (RSRQ),Received Signal Strength Indicator (RSSI), and a Channel StateInformation (CSI).
 7. The method of claim 1, wherein the informationregarding a signal configuration comprises a location of a resourceblock on which the first user equipment is receiving the referencesignal; wherein the resource block is outside of the transmissionbandwidth configuration of the second carrier but within the channelbandwidth of the second carrier.
 8. The method of claim 1, wherein theinformation regarding the signal configuration comprises a location of aresource block on which the first user equipment is receiving thereference signal; wherein the resource block is in a region of thesecond carrier, wherein the region is usable for low powertransmissions.
 9. The method of claim 1, wherein the resource block isoutside of the transmission bandwidth configuration of the secondcarrier, and wherein the resource block is within the channel bandwidthof a third carrier.
 10. The method of claim 9 wherein the channelbandwidth of the third carrier that is less than ⅓ of the channelbandwidth of the second carrier.
 11. The method of claim 9 wherein thethird carrier does not include a synchronization signal.
 12. The methodof claim 1, wherein the transmission bandwidth configuration of thesecond carrier has edge resource blocks, wherein the received signalconfiguration information indicates that the edge resource blocks areavailable to be used for direct wireless communication.
 13. The methodof claim 1, wherein the transmission bandwidth configuration of thesecond carrier has edge resource blocks, wherein the received signalconfiguration information indicates that a physical uplink controlchannel (PUCCH) is over-provisioned such that the edge resource blocksthat are normally used by the PUCCH are available to be used for directdevice-to-device communication.
 14. The method of claim 1, furthercomprising: receiving, in the first carrier, information regarding aresource of a third carrier, receiving, on the resource of the thirdcarrier, data from the second user equipment.
 15. The method of claim14, wherein the third carrier has a channel bandwidth and a transmissionbandwidth configuration; wherein the transmission bandwidthconfiguration of the third carrier is within the channel bandwidth ofthe third carrier; wherein the resource of the third carrier is withinthe channel bandwidth of the third carrier and proximate to an edge ofthe transmission bandwidth of the third carrier.
 16. The method of claim14, further comprising: receiving, on the first carrier, informationregarding a maximum transmission power limit for communication, on thethird carrier, between the first user equipment and the second userequipment.
 17. The method of claim 14, further comprising: determining,from the reference signal, a maximum transmission power limit forcommunication, on the third carrier, between the first user equipmentand the second user equipment.
 18. The method of claim 16, wherein thefirst user equipment limits its overall transmission power level basedthe maximum transmission power limit.
 19. The method of claim 1, whereinthe reference signal is a beacon signal specifically defined for D2Ddiscovery.
 20. A method in a first user equipment, the method comprisingreceiving, from a network entity and on a first carrier, informationregarding a signal configuration; receiving, a reference signal from asecond user equipment based on the signal configuration; wherein thereference signal is received within an aggregated channel bandwidthwherein the aggregated channel bandwidth includes a second carrier and athird carrier; wherein the second carrier has a first transmissionbandwidth configuration and the third carrier has a second transmissionbandwidth configuration, and the first and second transmission bandwidthconfigurations are contained within the aggregated channel bandwidth;wherein the reference signal is received outside both the firsttransmission bandwidth configuration and the second transmissionbandwidth configuration.
 21. A method in a first user equipment, themethod comprising: receiving, from a network entity and on a firstcarrier, information regarding a resource of a second carrier; whereinthe resource is within the channel bandwidth of the second carrier butoutside the transmission bandwidth configuration of the second carrier,wherein the first and second carriers are within a licensed spectrum,and receiving a reference signal from a second user equipment on theresource of the second carrier.
 22. The method of claim 21, furthercomprising camping on a wireless network, wherein the receiving stepsare performed after the camping step, but while the first user equipmentis still in an idle mode.
 23. The method of claim 21, further comprisingcommunicating with the network entity in an active mode, wherein thereceiving steps are performed while the first user equipment is in theactive mode.
 24. The method of claim 21, wherein the information isreceived in a system information block.
 25. A first user equipmentcomprising: a transceiver configured to receive, from a network entityand on a first carrier, information regarding a signal configuration; amemory communicatively linked to the transceiver, the memory beingconfigured to store the signal configuration; a processorcommunicatively linked to the memory and to the transceiver, theprocessor being configured to retrieve the signal configuration from thememory and, using the retrieved signal configuration, control thetransceiver to detect a reference signal of a second user equipment on asecond carrier.